This invention relates to a vaporizing and warming device for beverage-preparing machines, especially for household coffee machines of the type with a hot plate for keeping the thus-prepared beverage warm, a vaporizer tube carrying the water for the beverage, and a tubular heating element yielding the heat required for the vaporization and warming process. This heating element is thermally conductively connected with the vaporizer tube and is arranged together with the vaporizer tube on the underside of the hot plate.
In devices of this type it has been contemplated to arrange the vaporizer tube and the tubular heating element side-by-side and attached together to the underside of the hot plate. In another system it has been contemplated to dispose the tubular heating element and the vaporizer tube side-by-side in grooves of a solid hot plate and to fix the heating element and vaporizer tube in position by a flanging over of the groove rim. It has also been contemplated to cast the tubular heating element and the vaporizer tube into the hot plate, e.g. of aluminum.
Since the housings of such beverage-preparing machines generally consist of a synthetic resin (plastic), care must be taken that the hot plate, which is in contact with the housing or is arranged in the close vicinity thereof, does not reach a temperature leading to a discoloration, brittleness, or even destruction of the synthetic resin. In contrast to this prerequisite is the requirement that, on the one hand, the tubular heating element must possess the high temperature and heat transfer ability necessary for the evaporation of the water in the vaporizer tube, and, on the other hand, the hot plate is to assume a temperature sufficient to keep the beverage warm. These requirements, one contrary to the other, are not met under practical conditions, or are achieved to only an unsatisfactory degree, so that damage to the plastic housings occurs repeatedly, especially after a longer operating time.
This invention is based, at least in part, on the problem of fashioning a unit of the aforedescribed construction so that the plastic housing of the beverage-preparing machine does not suffer any damage and also does not become unattractive due to discoloration.
This problem is solved according to the invention by providing that the tubular heating element is arranged to be laterally offset with regard to the vaporizer tube and with the apex of the tubular heating element having a spacing from the hot plate which is smaller than the height of the vaporizer tube perpendicularly to the hot plate. Due to the fact that the tubular heating element is, on the other hand, connected with the vaporizer tube, and the latter is arranged on the underside of the hot plate, a heat transfer takes place from the tubular heating element via the vaporizer tube and/or the water contained therein to the hot plate. Inasmuch as the temperature of the water and/or of the steam in the vaporizer tube normally will not exceed 100.degree. C., the vaporizer tube assumes, at least at the locations where it is not heat-conductively connected with the tubular heating element, at most this temperature of the water or steam. This temperature, which thus is at most 100.degree. C., is further reduced due to the heat transfer to the hot plate, so that the hot plate, though having the temperature required to keep the beverage warm, does not assume such a temperature value which could lead to an impairment of the plastic housing.
The invention achieves still another effect. The hot plate according to preferred embodiments of the invention does not consist of solid, anodized aluminum but rather consists of a steel plate. Heretofore, such steel plates had to be aftertreated galvanically. Due to the fact that the invention has made a lower temperature possible and, in contrast to conventional systems, there are no local hot spots on the hot plate, the galvanic treatment can be replaced by a varnish (enamel) and/or paint application. This results, on the one hand, in savings during the manufacturing process and, on the other hand, provides novel esthetic design possibilities for such beverage-preparing machines.
According to one preferred embodiment of the invention, the vaporizer tube has a polygonal cross section and rests flat on the hot plate. This results in a good heat transfer for the hot plate. Furthermore, the invention makes it possible to employ tubular heating elements of greater efficiency, i.e. to obtain a more rapid vaporization, without the latter manifesting itself in a temperature increase at the hot plate.
Further, the present invention also contemplates embodiments with tubular heating element likewise fashioned to be polygonal. In this case, the element is advantageously arranged so that it faces the hot plate with one of its edges (edges at intersection of flat sides); thus, the radiant heat of the tubular heating element directly effective on the hot plate cannot lead, in turn, to local hot spots.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.